The present invention relates to addition compounds or salts thereof which are suitable for use as dispersing agents and as dispersion stabilizers and which can be obtained by reacting polyisocyanates, hydroxy compounds, compounds containing Zerewitinoff hydrogen and at least one nitrogen-containing, basic group and, if appropriate, compounds containing amine nitrogen, if appropriate in the presence of solvents and, if appropriate, in the presence of reaction catalysts.
The invention also relates to a process for the preparation of these addition compounds, to their use as dispersing agents and dispersion stabilizers and to pulverulent or fibrous solids which are to be incorporated into liquid systems and which have been coated with dispersing agents of this type.
Considerable mechanical forces are required in order to introduce solids into liquid media. In order to reduce these dispersion forces it is customary to use dispersing agents which facilitate incorporation. These are, in general, surface-active compounds, also known as surfactants, having an anion-active or cation-active structure or a nonionic structure. These compounds are either applied directly to the solid or added to the dispersion medium, in small amounts. The effort of dispersion is considerably reduced by means of a surfactant of this type.
It is also known that these solids tend to reagglomerate again after the dispersion process, because of mutual forces of attraction, which frustrates the dispersion effort previously applied and results in serious problems.
Inadequate dispersion makes itself evident by an increase in the viscosity of liquid systems, losses of gloss and shifts in color shade in paints and coatings, inadequate development of color strength in pigmented plastics and reduction in the mechanical strength of reinforced plastics.
Various dispersing agents have been suggested for solving these problems, for example in U.S. Pat. Nos. 3,788,996; 3,817,944; 4,029,861; 4,032,698; 4,048,207 and 4,070,388; West German Application No. DE 2,125,064; European Application Nos. EP 18,099 and EP 127,325; French Application No. FR 2,241,597; and British Application Nos. GB 1,339,930; GB 1,393,401 and GB 1,393,402. However, these dispersing agents only result in partial solutions of the problems in the art, in particular with regard to the flocculation-free miscibility of different pigments with one another, such as organic pigments and inorganic pigments. The pigment pastes prepared by the processes described also tend to interact with the surrounding medium, for example after being introduced into paints. It can thus be concluded that the adsorption layers built up do not possess adequate stability against desorption.
According to the most recent state of the art as described in European Patent Application No. EP 154,678, the aforementioned disadvantages can be largely overcome by employing the addition compounds suggested in that text. In some cases excellent results can be achieved by means of these addition compounds. As a result of changes in technology which have moved in recent years towards high-molecular weight binders, such as are used increasingly in so-called high-solids systems, water paints and systems which can be cured by UV and electron radiation, it has been established that these compounds are still not sufficiently compatible in binder systems of these types. This results in inadequate dispersion as a result of insufficient interaction with the binder and, in many cases, in sedimentation phenomena and associated dulling, speck formation and increases in viscosity.